Mechanism of delayed seed germination caused by high temperature during grain filling in rice (Oryza sativa L.)

Abstract

High temperature during grain filling considerably reduces yield and quality in rice (Oryza sativa L.); however, how high temperature affects seed germination of the next generation is not yet well understood. Here, we report that seeds from plants exposed to high temperature during the grain filling stage germinated significantly later than seeds from unstressed plants. This delay remained even after dormancy release treatments, suggesting that it was not due to primary seed dormancy determined during grain filling. In imbibed embryos of heat-stressed seeds, expression of abscisic acid (ABA) biosynthesis genes (OsNCEDs) was higher than in those of control seeds, whereas that of ABA catabolism genes (OsABA8′OHs) was lower. In the aleurone layer, despite no change in GA signaling as evidenced by no effect of heat stress on OsGAMYB gene expression, the transcripts of α-amylase genes OsAmy1C, OsAmy3B, and OsAmy3E were significantly down-regulated in heat-stressed seeds in comparison with controls. Changes in promoter methylation levels were consistent with transcriptional changes of ABA catabolism-related and α-amylase genes. These data suggest that high temperature during grain filling results in DNA methylation of ABA catabolism-related and α-amylase gene promoters, delaying germination of heat-stressed seeds.

ABA Metabolism and Homeostasis in Seed Dormancy and Germination

“…In rice ( Oryza sativa ), heat stress during seed filling has been described to delay germination even after dormancy release treatment and this delay is correlated with an increased expression of NCED genes and a decreased expression of CYP707A genes in imbibed seeds. Hot temperatures have been also shown to affect methylation of catabolism gene promoters and therefore have been suggested to influence catabolism gene expression, ABA levels and germination rates [ 79 ].…”

Seed Dormancy and Pre-Harvest Sprouting in Rice—An Updated Overview

“…DOG-1 boosts ABA signaling through interacting with the protein phosphatase 2C ABA HYPERSENSITIVE GERMINATION, where DOG-1 (by using DOG1–heme complex) inhibits its activity to elevate ABA sensitivity and imposes primary dormancy. Heat stress during grain filling had almost no effect on OsDOG1-like gene expression in imbibed embryos, but the genes OsNCED2 and OsABA8′OH3 play the most important roles in ABA biosynthesis [ 30 , 31 ]. During early grain filling, the resistant cultivars slow the seed germination and are independent of primary dormancy release, though susceptible cultivars generate greater grain chalkiness when subjected to heat stress [ 32 ].…”

“…During early grain filling, the resistant cultivars slow the seed germination and are independent of primary dormancy release, though susceptible cultivars generate greater grain chalkiness when subjected to heat stress [ 32 ]. DNA methylation of ABA catabolism-related and alpha amylase gene promoters inhibits the germination of heat-stressed embryos in plants toward abiotic stress, notably during the grain filling process [ 31 ]. The functions of two new genes, viz.…”

Enhancing crop diversity for food security in the face of climate uncertainty

“…Moderately elevated temperatures will affect all stages and processes of plant development (Lippmann et al., 2019). The expected adverse effects of high temperature on crop growth include decreased seed development and germination (Suriyasak et al., 2020), increased incidence of plant disease and herbivory (Ristaino et al., 2021), altered rates of respiration (Scafaro et al., 2021), photosynthesis (Moore et al., 2021) and photorespiration (Dusenge et al., 2019), and alterations in flowering time (Cao et al., 2021). Moreover, the effects of increased night‐time temperature are expected to be particularly detrimental for crop yield (Sadok and Jagadish, 2020).…”